Code P0420 clearing + smog test

[00PearlGT]

Ok so I recently purchased my 2000 mustang gt from a local guy. Monday morning while driving to work, I noticed the check engine light came on. I ended up pulling codes last night and came up with the usual P0420 catalyst code. I haven't checked the O2 sensor yet but I was wondering. If I clear the code before a smog test, will anything come up while its on the rollers? I'm getting a CA emissions test so its the total pita. I would go out and diagnose the issue but I have 10 days to smog and work full time. Also I was wondering. While driving the car I can hear fairly loud noise coming from the right side firewall similar to the sound of exhaust running through the pipes. This is my first time owning a GT so I was wondering if this is normal or if its a leak. The midpipe looks stock but it has some weird welds on the cats that doesn't look stock. Maybe a previous owner replaced the cats but I don't know.

Thanks

 

[LaserRed01GT]

P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

If you can hear a bonafide exhaust leak on bank 1 (passenger side) that could definitely be a contributor to the P0420 code.

Here is the description and causes:

P0420 Description

 

[thomas91169]

it prolly has high-flow cats. if thats the case, it wont pass the sniffer either.

where in cali are you located? i have the stock H pipe you can borrow if youre close enough.

 

[00PearlGT]

I'm located in Fremont. They better not be high flows cuz I do not want to deal with exhaust swapping anytime soon. I might just fix that leak if its a leak, then get it smogged and hope for the best. Smog is like $35 right?

 

[Dragstr05]

I can hear a sound that I would describe as exhaust running through the pipes, kinda sounds like the valves moving too...only does it at very low RPM in a higher gear than I could be. Has done it since stock, I kinda like the sound and its never caused a problem.

As for the code, you wont pass. If you clear it, it will reset the catalyst monitor. When you go to get your emissions, they wont pass it because the monitors arent complete. But as soon as the monitor completes, boom theres your P0420. A cheap solution would be to just throw some MIL's on there and forget about it, whether you have an aftermarket midpipe or not. You may need them eventually anyway.

 

[00PearlGT]

I'll probably take a look at the exhaust manifold, and midpipe for any leaks. Then if I can't find anything I'll pick up a new o2 sensor. If that doesn't fix it then I dunno. So I need to wait for the light to come back on, then fix the problem? I'm worried that I'll fix it but something will come up day of the smog.

 

[Mike97gt]

I'll probably take a look at the exhaust manifold, and midpipe for any leaks. Then if I can't find anything I'll pick up a new o2 sensor. If that doesn't fix it then I dunno. So I need to wait for the light to come back on, then fix the problem? I'm worried that I'll fix it but something will come up day of the smog.

I doubt it's the sensor but if you want to replace it then it's the one after the cat on the passenger side..

If it was my car I would put some MIL elims on and drive it untill the p1000 clears then try to go for the emmisions test.

 

[thomas91169]

i wouldnt get new ones, theyre expensive.

start off with some MIL's theyre cheap. always start small and work your way up with troubleshooting.

 

[MBDiagMan]

it prolly has high-flow cats. if thats the case, it wont pass the sniffer either.

where in cali are you located? i have the stock H pipe you can borrow if youre close enough.

I think this is correct. The ECM looks for a 100 degree Fahrenheit difference in temperature between cat input and cat output. It would stand to reason that a high flow cat would not generate as much heat, thus throwing the code.

That said, I'm not sure that just because the 100 degree temperature delta is not achieved means that the output from the cat is any dirtier for the sniffer test.

I am not familiar with the California test parameters, but if all they are looking at is tailpipe emissions it might pass. If, on the other hand, they will not pass if any codes are set, then you will have to take corrective action.

 

[00PearlGT]

So by installing some MIL's the rear o2 sensors will no longer throw codes and I'll be able to pass the "no ses light" portion. Now what happens when I go to the sniffer test? The previous owner says he never installed high flows and smogged the exact setup 2 years ago and passed.

 

[Mike97gt]

So by installing some MIL's the rear o2 sensors will no longer throw codes and I'll be able to pass the "no ses light" portion. Now what happens when I go to the sniffer test? The previous owner says he never installed high flows and smogged the exact setup 2 years ago and passed.

The ford eec is much tougher than the state smog test. Thats why in many states they don't bother with a sniffer if there is no codes in the system and all the emmisions monitors are passing.

try gettting the mil elims and drive around untill the P1000 clears ( I would give it a week) and then try to do the test. If it fails after that then you will probally need a cat converter, I am sure you can get a stock H on here CHEAP.

 

[thomas91169]

I am not familiar with the California test parameters, but if all they are looking at is tailpipe emissions it might pass. If, on the other hand, they will not pass if any codes are set, then you will have to take corrective action.

they wont even bother sticking it on the rollers if the CEL is on.

even if he stuck it on the rollers and it has high flow cats it wont pass the sniffer. My cobra had the bassani Catted Xpipe and bassani catback, it had two high-flow cats, and failed miserably. i mean, not even close, they couldve held the sniffer 2 feet from the tailpipe and it still wouldve failed. swapped with the stock H and passed beautifully.

btw to the original poster, where are you located in cali?

 

[LaserRed01GT]

they wont even bother sticking it on the rollers if the CEL is on.

even if he stuck it on the rollers and it has high flow cats it wont pass the sniffer. My cobra had the bassani Catted Xpipe and bassani catback, it had two high-flow cats, and failed miserably. i mean, not even close, they couldve held the sniffer 2 feet from the tailpipe and it still wouldve failed. swapped with the stock H and passed beautifully.

btw to the original poster, where are you located in cali?

I know lots of guys that have passed smog with high flow cats in California. But, you are right, they most likely will not even perform the test if the CEL is on. I think in CA the sniffer test is just part of the deal and is manadatory.

First try and resolve any exhaust leaks that you might have. Then you might try some O2 simulators or MIL eliminators as some call them.

The oxygen sensors are not thermistors so they have no idea what the exhaust gas temps are before and after the cats. They simply sample the oxygen content in the exhaust stream and compare it to a referenced sample. Oxygen is an inhibitor to electrical conductivity within the oxygen sensor. So the more the oxygen, the lower the electrical output, the less the oxygen the higher the electrical output.

 

[blubullett]

Whats up thomas!!! My names thomas too!!! And im in modesto too!!! And Ill donkey punch your sister too!!! J/k. Never seen anyone else from modesto in here. I heard that the magnaflows would pass.

 

[00PearlGT]

I'm located in Fremont. Can anyone provide me a picture of stock cats so I can get an idea. I looked under today and it looks like only the rear 2 cats were replaced. I doubt someone would only replace 2 cats with high flows and keep the other 2 stock. But he said that he passed on the current setup. I erased the code 2 days ago and it still hasn't come back. I'm going to the dmv to transfer the title so hopefully they give me 30 days to smog. I also found out that the air bag chime is on and the air bag light does not show up once turned to the on position. F***in lame. I've owned this car since saturday and its already pissing me off.